The objective of this research program is to investigate the anatomy of the primate limbic system in the rhesus monkey. The importance of investigating the structure and organization of this system derives from clinical reports that damage in humans causes serious deficits in memory and other cognitive functions. Results from laboratory investigations of non-human primates confirm the importance of the limbic system in these deficits. Our rationale for pursuing these investigations in the monkey is that the phylogenetically ancient structures of the limbic system have not been philogenetically stagnant but have, in concert with the expanding primate neocortex, undergone a progressive development. Previous results have shown that this has manifested itself anatomically in direct connections from the limbic system to the neocortex that are unique to the primate and afford potential modes for participation in "higher cortical functions" often thought to be the exclusive domain of the neocortex. We propose to continue this research program by investigating: 1) the topography and collateralization of cortical and subcortical efferents of the hippocampal formation; 2) the topography and collateralization of cortical and subcortical efferents of the amygdala; 3) the topography and collateralization of basal forebrain efferents to the thalamus, limbic system and neocortex; 4) the connections of the medial frontal cortex with the limbic system and thalamus; 5) the topography of afferent and efferent connections of the entorhinal, prorhinal and perirhinal cortices; and 6) the morphology and intrinsic connections of the hippocampal formation. These investigations will use standard histological, histochemical and Golgi impregnation procedures to identify the architectonics and morphology of these areas. Axonal connections will be studied using axon tracing techniques that rely upon the normal physiological process of axonal transport: injections of 3H-labeled amino acids will be made and autoradiographic procedures used to identify the sites of anterograde transport and injections of either horseradish peroxidase or fluorescent dyes will be made to identify the retrogradely labeled neurons.